The invention concerns a safety brake which is releasable via an electromagnet.
A safety requirement issued by regulatory bodies demands technical equipment to be provided with two separate braking circuits so that if one braking circuit should fail, a braking operation from the other braking circuit can be provided. This is the case for elevators constructed in accordance with elevator regulation TRA 200 DIN EN 81.
In accordance with the subject matter of German Gebrauchmuster 295 10 828 two brakes are spacially integrated. In this arrangement there are two armatures, two brake disks, two spring arrangements that press the armature disks against the brake disks, and a single electromagnet with a magnetic coil arranged between the armature disks and brake disks. This arrangement provides a functionally safe, inexpensive and compact system that provides two brakes that are independent of one another.
In order to save space and to simplify the brakes while maintaining the safety function of a braking operation, and thereby reduce the cost of brakes, these brakes were further developed as shown in German Gebrauchmuster 296 11 732.3. In this brake the electromagnet comprises a magnetic coil and coil carrier that surrounds a central shaft that is arranged to be axially displaceable, but not rotatable in the brake. In addition, a single armature disk 3 that is axially displaceable, but cannot be rotated in the brake, is arranged axially between one of two brake disks 2, 11 and the magnetic coil/coil carrier. Springs are tensioned axially between the magnetic coil/coil carrier and the single armature disk 3.
A disadvantage of this twin circuit brake is that, on account of the placement of the magnetic coil in the region between the rotating brake disks, the heat that is generated on the brake disks during braking bears upon the coil from two sides. Thus, the coil is heated in accordance with the amount of frictional work done during braking. This heating can become significant, particularly in a high temperature environment, for example in warm countries. In order to prevent overheating of the coil it is necessary to limit the braking power correspondingly.
A further disadvantage of this twin circuit brake is that it is necessary to change the entire coil when the brake linings are changed. This means that an inconvenient amount of effort needs to be expended in order to change the parts subject to wear.
Obviously, this twin circuit brake also needs to comply with the aforementioned safety requirement. In particular, malfunction situations (jamming or seizure situations) that can affect the movable parts of the brake should be accounted for.